A lot of us cave divers work in other areas as well - I'm an engineer in Oil & Gas - a lot of other folks I know are either scientists or engineers. This sort

A lot of us cave divers work in other areas as well - I'm an engineer in Oil & Gas - a lot of other folks I know are either scientists or engineers. This sort of activity appeals to us for some reason. You described a blowout preventer (https://en.wikipedia.org/wiki/Blowout_preventer https://en.wikipedia.org/wiki/Blowout_preventer) by the way :) Many cave systems are quite shallow, and while I don't know the details on the one there in Mallorca, by the size of what's described it was probably above the water table even though there likely wasn't a free-air connection to the surface.